The invention relates generally to processes for manufacturing integrated circuits and other electronic devices. More specifically, the invention relates to precleaning processes for removing native oxide from an area of a metal layer that is exposed by an opening in an overlying dielectric, so that the opening subsequently can be filled by a metal plug.
A common process sequence in manufacturing integrated circuits and other electronic devices is to deposit a number of metal conductors on a substrate, then cover the metal with a dielectric layer, then etch a number of openings in the dielectric so that each opening exposes a contact area on one of the metal conductors, then deposit a metal plug in each opening so as to make electrical contact with the contact area. If the substrate is exposed to the ambient atmosphere or any other source of oxygen after the openings are formed, the surface of the semiconductor or metal layer exposed in each opening will become oxidized. This native oxide must be removed or xe2x80x9ccleanedxe2x80x9d before depositing the metal plug in order to achieve good electrical contact between the plug and the contact area. The process of removing native oxide from a metal conductor before depositing a metal plug is commonly termed xe2x80x9cprecleaningxe2x80x9d.
A serious shortcoming of conventional precleaning processes for metal conductors is that the precleaning process can damage the dielectric. Particularly susceptible to damage are xe2x80x9clow-xcexaxe2x80x9d dielectric materials that incorporate carbon atoms to reduce their dielectric constant xe2x80x9cxcexaxe2x80x9d. We have measured an increase in the dielectric constant of such materials after performing a precleaning process.
The invention is a precleaning process suitable for fabricating metal plugs in a low-xcexa, carbon-containing dielectric. More specifically, the invention is a process for cleaning a contact area of a metal conductor on a semiconductor workpiece so as to minimize damage to a carbon-containing dielectric overlying the metal. After forming contact openings in the dielectric so as to expose contact areas on the underlying metal conductor, the contact areas are cleaned by exposing the workpiece to a plasma formed from a mixture of hydrogen-containing and helium gases.
Surprisingly, our hydrogen-helium plasma process can repair damage to the dielectric caused by preceding process steps. Accordingly, another aspect of our invention is a method of using such plasma process to repair damage to a carbon-containing dielectric on a semiconductor workpiece caused by an oxygen plasma process for stripping resist from the surface of the dielectric.